Although numerous buildings having glass windows and smooth walls have been constructed for several ten or hundred years, no or less intensive research has been made for developing a method for efficiently cleaning such glass windows and smooth walls. For this reason, cleaning of glass windows and smooth walls has been done using manual labor.
It, however, involves many problems. For example, it is time consuming and exposes a person who performs such cleaning task to a danger of falling. In particular, in case of cleaning a window of an apartment building, water used in the cleaning may flow downwards, thereby causing the water to soil the outer surfaces of windows on the lower stories.
To solve the above-mentioned problems, wall/window cleaning robots have been proposed, for example, in Korean Utility Model Registration No. 20-0265415 and Korean Patent No. 10-0632260.
The prior art wall/window cleaning robots, however, still do not solve the above-mentioned problems; for instance, water used in a cleaning operation may flow downwards. Furthermore, they are so large and heavy that they can be separated from an outer wall/window during cleaning operation. That is, they cannot freely move along the outer surface of a window or outer wall while being stably vacuum-sucked onto the outer surface. More seriously, they have a structure that necessarily stops the movement intermittently, thereby leaving undesirable spots after the cleaning operation is completed. Moreover, they cannot clean a dead zone of the outer wall/window because they need too large a radius of rotation to change their movement direction, resulting in unsatisfactory cleaning. For various reasons including the above-mentioned problems, no prior art cleaning robots have been successfully practically applied.
The above information disclosed in this Background Art section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.